Download The Nervous System

The Nervous System
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Functions of the Nervous System
1. Sensory input – gathering
information
 To monitor changes
occurring inside and
outside the body
(changes = stimuli)
2. Integration –
 to process and interpret
sensory input and decide
if action is needed.
3. Motor output
 A response to integrated
stimuli
 The response activates
muscles or glands
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.1a
Structural Classification of the
Nervous System
 Central nervous system
(CNS)
 Brain and spinal cord
 Develops from the
embryonic neural tube
 Peripheral nervous system
(PNS)
 Nerve and ganglia
outside the brain and
spinal cord
 Nerves are neuron
fibers bundled together
by connective tissue
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.2
Functional Classification of the Peripheral
Nervous System
 Sensory (afferent)
division
 Nerve fibers that
carry information to
the central nervous
system
 Motor (efferent) division
 Nerve fibers that
carry impulses away
from the central
nervous system
 Two subdivisions
 Somatic nervous
system = voluntary
 Autonomic
nervous system =
involuntary
Slide 7.3a
Nervous Tissue: Support Cells
(Neuroglia or Glia)
 Astrocytes
 Abundant, star-shaped cells
 Brace neurons
 Form barrier
between capillaries
and neurons
 Control the chemical
environment of
the brain (CNS)
 Microglia (CNS)
 Spider-like phagocytes
 Dispose of debris
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Slide 7.5
Nervous Tissue: Support Cells
 Ependymal cells (CNS)
 Line cavities of the
brain and spinal cord
 Circulate
cerebrospinal
fluid
 Oligodendrocytes(CNS)
 Produce myelin sheath
around nerve fibers in the
central nervous system
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.6
Support Cells of the PNS
 Satellite cells
 Protect neuron cell bodies
 Schwann cells
 Form myelin sheath in the peripheral
nervous system
Figure 7.3e
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.7b
Nervous Tissue: Neurons
 Neurons = nerve cells
 Cells specialized to transmit messages
 Major regions of neurons
 Cell body – nucleus and metabolic center
of the cell
 Processes – fibers that extend from the
cell body (dendrites and axons)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.8
Neuron Anatomy
 Cell body
 Nucleus
 Large nucleolus
 Extensions outside the
cell body
 Dendrites – conduct
impulses toward the
cell body
 Axon – conduct
impulses away from
the cell body (only
1!)
Figure 7.4a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.10
Axons and Nerve Impulses
 Axons end in axonal
terminals
 Axonal terminals contain
vesicles with
neurotransmitters
 Axonal terminals are
separated from the next
neuron by a gap
 Synaptic cleft – gap
between adjacent
neurons
 Synapse – junction
between nerves
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.11
Functional Classification of
Neurons
 Sensory (afferent) neurons
 Carry impulses from the sensory receptors
 Cutaneous sense organs
 Proprioceptors – detect stretch or tension
 Motor (efferent) neurons
 Carry impulses from the central nervous system
 Interneurons (association neurons)
 Found in neural pathways in the central nervous system
 Connect sensory and motor neurons
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Neuron Classification
Figure 7.6
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Slide 7.15
Structural Classification of Neurons
 Multipolar
neurons – many
extensions from
the cell body
 Bipolar neurons –
one axon and one
dendrite
 Unipolar neurons
– have a short
single process
leaving the cell
body
How Neurons Function
(Physiology)
 Irritability – ability to respond to stimuli
 Conductivity – ability to transmit an
impulse
 The plasma membrane at rest is
polarized
 Fewer positive ions are inside the cell than
outside the cell
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.17
Starting a Nerve Impulse
 Depolarization – a
stimulus depolarizes the
neuron’s membrane
 A deploarized
membrane allows
sodium (Na+) to flow
inside the membrane
 The exchange of ions
initiates an action
potential in the neuron
Figure 7.9a–c
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.18
The Action Potential
 If the action potential (nerve impulse)
starts, it is propagated over the entire
axon
 Potassium ions rush out of the neuron
after sodium ions rush in, which
repolarizes the membrane
 The sodium-potassium pump restores
the original configuration
 This action requires ATP
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.19
Nerve Impulse Propagation
 The impulse
continues to move
toward the cell body
 Impulses travel
faster when fibers
have a myelin
sheath
Figure 7.9c–e
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.20
Continuation of the Nerve Impulse
between Neurons
 Impulses are able to cross the synapse
to another nerve
 Neurotransmitter is released from a nerve’s
axon terminal
 The dendrite of the next neuron has
receptors that are stimulated by the
neurotransmitter
 An action potential is started in the dendrite
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.21
How Neurons Communicate at
Synapses
Figure 7.10
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.22
Regions of the Brain
 Cerebral hemispheres
 Diencephalon
 Sits on top of the
brain stem and is
enclosed by the
cerebral heispheres
 Made of three parts:
thalamus,
hypothalamus,
epithalamus
 Brain stem
 Attaches to the
spinal cord
 Includes the
midbrain, pons, and
medulla oblongata
 Cerebellum
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 7.12
Slide 7.27
Structure of the Cerebrum
 Fissures (deep grooves)
divide the cerebrum into
lobes
 Surface lobes of the
cerebrum include:
frontal lobe, parietal
lobe, occipital lobe, and
temporal lobe
 Paired (left and right)
superior parts of the
brain
 Include more than half
of the brain mass
 The surface is made of
ridges (gyri) and
grooves (sulci)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Specialized Areas of the Cerebrum
 Somatic sensory area – receives impulses from the body’s
sensory receptors
 Primary motor area – sends impulses to skeletal muscles
 Broca’s area – involved in our ability to speak
 Cerebral areas involved in special senses include: gustatory
area (taste), visual area, auditory area, and olfactory area
 Interpretation areas of the cerebrum
 Speech/language region
 General interpretation area
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.30
Specialized Area of the Cerebrum
Figure 7.13c
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Slide
Sensory and Motor Areas of the
Cerebral Cortex
Figure 7.14
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.31
Layers of the Cerebrum
 Gray matter
 Outer layer that is
composed mostly of
neuron cell bodies
 White matter
 Fiber tracts (bundles of
nerve fibers) that carry
impulses to and from the
cortex inside the gray
matter
 Example: corpus callosum
connects hemispheres
 Basal nuclei – internal islands
of gray matter
 Regulates voluntary motor
activities by modifying info
sent to the motor cortex
Thalamus
 Surrounds the third
ventricle
 The relay station for
sensory impulses
 Transfers impulses to
the correct part of the
cortex for localization
and interpretation
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.35
Hypothalamus
 Under the thalamus
 Important autonomic nervous
system center
 Helps regulate body
temperature
 Controls water balance
 Regulates metabolism
 An important part of the limbic
system (emotions)
 The pituitary gland is attached
to the hypothalamus
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Cerebellum
 Two
hemispheres
with convoluted
surfaces
 Provides
involuntary
coordination of
body
movements
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Medulla Oblongata
 The lowest part of the brain
stem
 Merges into the spinal cord
 Includes important fiber
tracts
 Contains important control
centers
 Heart rate control
 Blood pressure
regulation
 Breathing
 Swallowing
 Vomiting
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.41
Pons
 The bulging
center part
of the brain
stem
 Mostly
composed of
fiber tracts
 Includes
nuclei
involved in
the control of
breathing
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.40
Meninges
 Three connective tissue layers
that cover and protect the brain
and spinal cord.
 Dura mater
 Double-layered external
covering
 Periosteum – attached to
surface of the skull
 Meningeal layer – outer
covering of the brain
 Folds inward in several areas
to connect brain to cranial
cavity.
 Arachnoid layer
 Middle layer that is web-like
 Pia mater
 Internal layer that clings to
the surface of the brain and
spinal cord
Slide
Spinal Cord
 Extends from the
medulla oblongata to the
region of T12
 Provides conduction
pathway to (ascending)
and from (descending)
the brain and is a major
reflex center.
Figure 7.18
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.52
Spinal Cord
 Exterior white mater – conduction tracts
 Internal gray matter - mostly cell bodies
 Dorsal (posterior) horns contain cell bodies of sensory
neurons
 Anterior (ventral) horns contain cell bodies of motor neurons
 Central canal filled with cerebrospinal fluid
 Meninges cover the spinal cord for cushion and protection
 Nerves leave at the level of each vertebrae
Structure of a Nerve
 Endoneurium surrounds each fiber
 Groups of fibers are bound into
fascicles by perineurium
 Fascicles are bound together by
epineurium
 Mixed nerves – both sensory and
motor fibers
 Afferent (sensory) nerves – carry
impulses toward the CNS
 Efferent (motor) nerves – carry
impulses away from the CNS
 12 pairs of cranial nerves serve
the head and neck with only one
(the vagus nerve) extending to the
thoracic and abdominal cavity.
 There 31 pairs of spinal nerves
that exit at the junctions between
vertebrae.
Autonomic Nervous System
 The involuntary branch of the nervous system that consists of
only motor nerves. Divided into two sections: sympathetic and
parasympathetic.
Autonomic Functioning
 Sympathetic – “fight-orflight”
 Response to unusual
stimulus
 Takes over to
increase activities
 Remember as the “E”
division = exercise,
excitement,
emergency, and
embarrassment
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Slide
Autonomic Functioning
 Parasympathetic –
housekeeping activites
 Conserves energy
 Maintains daily
necessary body
functions
 Remember as the
“D” division digestion,
defecation, and
diuresis
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Slide
The Reflex Arc
 Reflex – rapid, predictable, and
involuntary responses to stimuli
 Reflex arc – direct route from a sensory
neuron, to an interneuron, to an effector
Figure 7.11a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.23
Types of Reflexes and Regulation
 Autonomic reflexes
 Smooth muscle
regulation
 Heart and blood
pressure
regulation
 Regulation of
glands
 Digestive system
regulation
 Somatic reflexes
 Activation of
skeletal muscles
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.25
The Senses
 General senses of touch (tactile)
 Temperature- thermoreceptors (heat)
 Pressure- mechanoreceptors (movement)
 Pain- mechanoreceptors
 Special senses
 Smell- chemoreceptors (chemicals)
 Taste- chemoreceptors
 Sight- photoreceptors (light)
 Hearing- mechanoreceptors
 Equilibrium- (balance) mechanoreceptors
The Eye and Vision
 70 percent of all sensory
receptors are in the eyes
 Each eye has over a million
nerve fibers
 Protection for the eye
 Most of the eye is
enclosed in a bony orbit
made up of the lacrimal
(medial), ethmoid
(posterior), sphenoid
(lateral), frontal
(superior), and zygomatic
and maxilla (inferior)
 A cushion of fat
surrounds most of the
eye
Accessory Structures of the Eye
 Eyelids- brush
particles out of eye
or cover eye
 Eyelashes- trap
particles and keep
them out of the eye
 Ciliary glands –
modified
sweat glands
between the
eyelashes- secrete
acidic sweat to kill
bacteria, lubricate
eyelashes
Accessory Structures of the Eye
 Conjunctiva
 Membrane that lines the eyelids
 Connects to the surface of the eye- forms a seal
 Secretes mucus to lubricate the eye
http://neuromedia.neurobio.ucla.edu/campbell/eyeandear/wp_images/175_conjunctiva.gif
Accessory Structures of the Eye
 Lacrimal apparatus
 Lacrimal gland –
produces lacrimal fluid
 Lacrimal canals –
drains lacrimal fluid
from eyes
 Lacrimal sac –
provides passage of
lacrimal fluid towards
nasal cavity
 Nasolacrimal duct –
empties lacrimal fluid
into the nasal cavity
 Lacrimal fluid contains
anibodies and
lysozyme to protect,
moisten, and lubricate
the eye
Extrinsic Eye Muscles
 Muscles attach to the outer
surface of the eye that
produce eye movements
 Superior oblique- eyes
look out and down
 Superior rectus- eyes
looks up
 Lateral rectus- eyes look
outward
 Medial rectus- eyes look
inward
 Inferior rectus- eyes
looks down
 Inferior oblique- eyes
look in and up
Structure of the Eye
 The wall is composed of three tunics
 Fibrous tunic –
outside layer
 Choroid –
middle
layer
 Sensory
tunic –
inside
layer
The Fibrous Tunic
 Sclera
 White connective tissue layer
 Seen anteriorly as the “white of the eye”
 Semi-transparent
The Fibrous Tunic
 Cornea
 Transparent, central anterior portion
 Allows for light to pass through (refracts, or bends, light slightly)
 Repairs itself easily
 The only human tissue that can be transplanted without fear of
rejection
Choroid Layer
 Blood-rich nutritive tunic
 Pigment prevents light from scattering (opaque- blocks light
from getting in, has melanin)
 Modified interiorly into two structures
 Cilliary body – smooth muscle (contracts to adjust the
shape of the lens)
 Iris- pigmented layer that gives eye color (contracts to
adjust the size of the pupil- regulates entry of light into the
eye)
 Pupil – rounded opening in the iris
Sensory Tunic (Retina)
 Contains receptor cells (photoreceptors)
 Rods
 Cones
 Signals leave the retina toward the brain through the optic
nerve
Neurons of the Retina and Vision
 Rods
 Most are found towards the
edges of the retina
 Allow dim light vision and
peripheral vision (more
sensitive to light, do not
respond in bright light)
 Perception is all in gray
tones
 Cones
 Allow for detailed color
vision
 Densest in the center of the
retina
 Fovea centralis – area of
the retina with only cones
 Respond best in bright light
 No photoreceptor cells are at
the optic disk, or blind spot
Cone Sensitivity
 There are three types of
cones
 Different cones are
sensitive to different
wavelengths
 Red-long
 Green-medium
 Blue-short
 Color blindness is the
result of lack of one or
more cone type
How do we see colors?
• To see any color, the brain must compare the input from
different kinds of cone cells—and then make many other
comparisons as well.
• The lightning-fast work of judging a color begins in the
retina, which has three layers of cells. Signals from the
red and green cones in the first layer are compared by
specialized red-green "opponent" cells in the second layer.
These opponent cells compute the balance between red
and green light coming from a particular part of the visual
field. Other opponent cells then compare signals from blue
cones with the combined signals from red and green
cones.
COLORBLINDNESS
- An inherited trait that is
transferred on the sex
chromosomes (23rd pair)sex-linked trait
- Occurs more often in
males
- Can not be cured or
corrected
•Comes from a lack of one or
more types of color receptors.
•Most are green or red or both
and that is due to a lack of red
receptors.
•Another possibility is to have
the color receptors missing
entirely, which would result in
black and white vision.
COLORBLINDNESS TEST PLATES
http://www.geocities.com/Heartland/8833/coloreye.html
Lens
 Biconvex crystallike structure
 Held in place by a
suspensory
ligament attached
to the ciliary body
 Refracts light
greatly
Internal Eye Chamber Fluids
 Aqueous humor
 Watery fluid found in
chamber between the lens
and cornea
 Similar to blood plasma
 Helps maintain intraocular
pressure
 Provides nutrients for the
lens and cornea
 Reabsorbed into venous
blood through the canal of
Schlemm
Refracts light
slightly
Internal Eye Chamber Fluids
 Vitreous humor
 Gel-like substance behind the lens
 Keeps the eye from collapsing
 Lasts a lifetime and is not replaced
Refracts light
slightly
Holds lens and
retina in place
http://faculty.washington.edu/kepeter/119/images/eye3.jpg
Lens Accommodation
 Light must be focused to a point
on the retina for optimal vision
 The eye is set for distance
vision
(over 20 ft away)
 20/20 vision- at 20 feet, you see
what a normal eye would see at
20 feet (20/100- at 20, normal
person would see at 100)
 The lens must change shape to
focus for closer objects
 If the image is focused at the spot
where the optic disk is located,
nothing will be seen. This is
known as the blind spot. There are
no photoreceptors there, as nerves
and blood vessels pass through this
point.
Visual Pathway
 Photoreceptors of the retina
 Optic nerve
 Optic nerve crosses at the
optic chiasma
 Optic tracts
 Thalamus (axons form optic
radiation)
 Visual cortex of the occipital
lobe
MYOPIA
Nearsightedness, or myopia is the difficulty of seeing
objects at a distance.
Myopia occurs when the
eyeball is slightly longer
than usual from front to
back. This causes light
rays to focus at a point in
front of the retina, rather
than directly on its
surface.
Concave lenses are used to
correct the problem.
HYPEROPIA
Hyperopia, or
farsightedness, is when
light entering the eye
focuses behind the retina.
Hyperoptic eyes are
shorter than normal.
Hyperopia is treated using
a convex lens.
http://web.mountain.net/~topeye/images/hyperopia.jpg
Eye Reflexes
 Internal muscles are controlled by the autonomic nervous
system
 Bright light causes pupils to constrict through action of
radial (iris) and ciliary muscles
 Viewing close objects causes accommodation
 External muscles control eye movement to follow objectsvoluntary, controlled at the frontal eye field
 Viewing close objects causes convergence (eyes moving
medially)
The Ear
 Houses two senses
 Hearing (interpreted
in the auditory
cortex of the
temporal lobe)
 Equilibrium (balance)
(interpreted in the
cerebellum)
 Receptors are
mechanoreceptors
 Different organs house
receptors for each
sense
Anatomy of the Ear
 The ear is divided into three areas
 Outer
(external)
ear
 Middle
ear
 Inner
ear
The External Ear
 Involved in hearing only
 Pinna (auricle)- collects
sound
 External auditory canalchannels sound inward
 Narrow chamber in the
temporal bonethrough the external
auditory meatus
 Lined with skin
 Ceruminous (wax)
glands are present
 Ends at the tympanic
membrane (eardrum)
The Middle Ear or Tympanic Cavity
 Air-filled cavity within the temporal bone
 Only involved in the sense of hearing
 Two tubes are associated with the inner ear
 The opening from the auditory canal is covered by the
tympanic membrane (eardrum)
 The auditory tube connecting the middle ear with the throat
(also know as the eustacian tube)
 Allows for equalizing pressure during yawning or
swallowing
 This tube is otherwise collapsed
Bones of the Tympanic Cavity
 Three bones span the
cavity
 Malleus (hammer)
 Incus (anvil)
 Stapes (stirrip)
 Vibrations from
eardrum move the
malleus
 These bones transfer
sound to the inner ear
Inner Ear or Bony Labyrinth
 Also known as osseous labyrinth- twisted bony
tubes
 A maze of bony chambers within the temporal bone
 Cochlea
 Upper chamber is the scala vestibuli
 Lower chamber is the scala tympani
 Vestibule
 Semicircular canals
 Includes sense organs for hearing and balance
 Filled with perilymph
 Vibrations of the stapes push and pull
on the membranous oval window, moving
the perilymph through the cochlea. The round
window is a membrane at the opposite end to relieve
pressure.
Organ of Corti
 Located within the cochlea
 Receptors = hair cells on the basilar membrane
 Gel-like tectorial membrane is capable of bending hair cells
(endolymph in the membranous labyrinth of the cochlear
duct flows over it and pushes on the membrane
 Cochlear nerve attached to hair cells transmits nerve impulses to
auditory cortex on temporal lobe
Scala tympani
Mechanisms of Hearing
 Vibrations from sound waves move tectorial membrane (pass
through the endolymph fluid filling the membranous
labyrinth in the cochlear duct)
 Hair cells are bent by the membrane
 An action potential starts in the cochlear nerve
 The signal is transmitted to the midbrain (for auditory
reflexes and then directed to the auditory cortex of the
temporal lobe)
 Continued stimulation can lead to adaptation (over stimulation to the
brain makes it stop interpreting the sounds)
Organs of Equilibrium
 Receptor cells are in two structures
 Vestibule
 Semicircular canals
 Equilibrium has two functional parts
 Static equilibrium- in the vestibule
 Dynamic equilibrium- in the semicircular canals
Static Equilibrium
 Maculae – receptors in
the vestibule
 Report on the
position of the head
 Send information via
the vestibular nerve
 Anatomy of the
maculae
 Hair cells are
embedded in the
otolithic membrane
 Otoliths (tiny stones)
float in a gel around
the hair cells
 Movements cause
otoliths to bend the hair
cells (gravity moves the
“rocks” over and pulls
the hairs)
Dynamic Equilibrium
 Whole structure is the ampulla
 Crista ampullaris – receptors in the
semicircular canals
 Tuft of hair cells
 Cupula (gelatinous cap) covers the
hair cells
 Action of angular head movements
 The cupula stimulates the hair cells
 Movement of endolymph pushes
the cupula over and pulls the
hairs
 An impulse is sent via the vestibular
nerve to the cerebellum
Chemical Senses – Taste and
Smell
 Both senses use chemoreceptors
 Stimulated by chemicals in solution
 Taste has four types of receptors
 Smell can differentiate a large range of
chemicals
 Both senses complement each other
and respond to many of the same
stimuli
Olfaction – The Sense of Smell
 Olfactory receptors are in the roof of the nasal cavity
 Neurons with long cilia
 Chemicals must be dissolved in mucus for
detection
Olfaction – The Sense of Smell
 Impulses are transmitted via the olfactory nerve
 Interpretation of smells is made in the cortex
(olfactory area of temporal lobe)
The Sense of Taste
 Taste buds
house the
receptor
organs
 Location of
taste buds
 Most are on
the tongue
 Soft palate
 Cheeks
The Tongue and Taste
 The tongue is covered
with projections called
papillae
 Filiform papillae – sharp
with no taste buds
 Fungifiorm papillae –
rounded with taste buds
 Circumvallate papillae –
large papillae with taste
buds
 Taste buds are found on
the sides of papillae
http://neuromedia.neurobio.ucla.edu/campbell/oral_cavity/wp_images/96_fungiform.gif
Structure of Taste Buds
 Gustatory cells are the receptors
 Have gustatory hairs (long microvilli)
 Hairs are stimulated by chemicals dissolved in saliva
Structure of Taste Buds
 Impulses are carried to the
gustatory complex (pareital
lobe) by several cranial
nerves because taste buds
are found in different areas
 Facial nerve
 Glossopharyngeal nerve
 Vagus nerve
Taste Sensations
 Sweet receptors
 Sugars
 Saccharine
 Some amino acids
 Sour receptors
 Acids
 Bitter receptors
 Alkaloids
 Salty receptors
 Metal ions
 Umami
 Glutamate, aspartate, MSG, meats)
http://instruct1.cit.cornell.edu/courses/psych431/student2000/mle6/tonguebig.gif